macOS shell script to upgrade multi-user nix installs

nixup.sh

#!/bin/sh
# see https://nixos.org/manual/nix/stable/installation/upgrading.html
set -eu

if [ "$(id -u)" != 0 ]; then
  script="$(basename "$0")"
  >&2 echo "$script: root required, re-executing through sudo"
  exec sudo --login "$0"
fi

cmd() {
  printf "[#] \033[36m%s\033[0m\n" "$*"
  "$@"
}

cmd nix-channel --update
cmd nix-env -iA nixpkgs.nix

# the documentation on post-upgrade nix-daemon restarts seems to be slightly
# wrong; `launchctl remove` won't wait until jobs have actually stopped. if i
# follow the documentation exactly, `launchctl load` will sometimes run before
# the old nix-daemon is gone. the unload-load-method i'm using here appears to
# be working for me as of macOS 12.4.

plist=/Library/LaunchDaemons/org.nixos.nix-daemon.plist

cmd launchctl unload "$plist"
cmd launchctl load -w "$plist"